German Patent Application No. DE 42 27 893 describes a differential-pressure sensor, which has two semiconductor diaphragms. The semiconductor diaphragms are each provided with interconnected piezoresistive resistors on the upper side. To protect the sensitive sensor elements, the upper sides of the semiconductor diaphragms are situated in a common reference chamber, which can be hermetically sealed.
In addition to the measurement of a differential pressure, the measurement of an absolute pressure with the aid of micromechanical pressure sensors is also known from the related art. Thus, for example, German Patent Application No. DE 100 32 579 describes the manufacture of such an absolute-pressure sensor, where a cavity and a diaphragm situated above the cavity are produced, using variably porosified regions and subsequent thermal treatment. German Patent Application No. DE 101 38 759 describes an elaboration on this principle, where variably doped regions are used for producing the cavity and the diaphragm.
A method, by which both a differential-pressure sensor and an absolute-pressure sensor can be manufactured, is known from German Patent Application No. DE 100 32 579. In a first step, a first porous layer is initially formed in a semiconductor substrate, and in a second step, a hollow space or cavity is formed under or from the first porous layer in the semiconductor substrate, using an external access opening.
In very general terms, the pressure signals of a micromechanical pressure sensor may be acquired on the diaphragm, using both capacitive dielectric layers and piezoresistive resistors. In this context, an evaluation circuit may be mounted in direct proximity to the sensor element necessary for detecting the pressure signal, on the same substrate as the sensor element.